Fluoroaryl phosphate esters



United States Patent Oflice Patented May 21, 1968 ABSTRACT OF THEDISCLOSURE Triaryl phosphates of which the aryl groups include at leastone monofluorinated aryl group, useful particularly at elevatedtemperatures as hydraulic. fluids, lubricants and heat transfer orcooling media, for aircraft systems and for industrial use. Typicalpreferred compounds include m-fluorophenyl diphenyl phosphate andm-fluorophenyl p-fluorophenyl phenyl phosphate.

This invention relates to certain fluoroaryl phosphate esters and isparticularly concerned with the provision of novel fluorinated triarylphosphates.

It is an object of the present invention to provide a series ofcompounds having high fire resistance, high temperature stability, andwhich remain in liquid form over a wide temperature range and arerelatively nonvolatile at elevated temperatures.

Another object of the invention is the provision of fluorinated triarylphosphate esters having the above-noted properties and other advantages,and having particular ,I

utility as hydraulic fluids or components thereof, heat transfer fluids,and as lubricants.

Other objects and advantages will appear hereinafter. We have discoveredthat the above-noted objects are achieved according to the invention bythe provision of a class of fluoroaryl phosphates having the formulawhere R is a member selected from the group consisting ofmonofluorophenyl, monofluorocresyl and monofluoroxylyl, and R and R" areeach a member selected from the group consisting of phenyl, cresyl,xylyl, monofluorophenyl, monofluorocresyl and monofluoroxylyl. R and Rcan be the same or different.

The fluorine substituent can be carried in ortho, meta or para positionon the phenyl, cresyl or xylyl nucleus, with respect to the attachmentof such nucleus to the oxygen atom of the phosphate ester. However, themeta fluoro derivatives generally are preferred because such metafluoroaryl phosphate esters according to the invention have a widerliquid range and a lower melting point as compared to the correspondingpara and ortho derivatives.

According to the above general formula and as will be apparent furtherhereinafter, the fluorinated triaryl phosphate esters of the inventioncan include esters having only one fluoroaryl, e.g., fluorophenyl,group, two fluoroaryl groups or three fluoroaryl groups. Compounds whichcontain fluorophenyl groups are preferred over those containingfluorocresyl or fluoroxylyl groups. Where the phosphate esters of theinvention contain cresyl or xylyl groups, it is preferred that the esteralso contain at least one phenyl group. The preferred esters further arethose which contain fluorophenyl groups as compared to those containingfluorocresyl or fluoroxylyl groups. Thus, where the ester containsphenyl, and also cresyl and/or xylyl groups, it is preferred that atleast the phenyl group be monofluorinated.

The preferred triaryl phosphate esters of the invention are themonofluorophenyl diphenyl phosphates, the his- (monofluorophenyDphenylphosphates, and the tris- (monofluoro-phenyl)phosphates. Such compoundshave the general formula where X is a member selected from the groupconsisting of hydrogen and fluorine, there being at least one fluorineatom in the molecule and said fluorine atom or atoms preferably being inmeta position in the phenyl nuclei.

It has been found that the above-defined fluoroaryl phosphates areparticularly valuable as functional fluids, e.g., as base stocks forhydraulic fluids, and are also useful as heat transfer media and aslubricants due to the advantageous physical properties of suchcompounds. These properties include high fire resistance, increasedtemperature stability, and liquidity over a relatively wide temperaturerange. Thus, for example, generally these fluorinated phosphate estershave a thermal stability in the range of about 600- to about 800 F.,autoignition temperatures of the order of about 900 to about 1,000 F.and remain liquid down to a temperature of the order of about 60 F.Further, the viscosity of such fluoroaryl phosphate esters at lowtemperatures of the order of -25 to 40 F. permits the operative use ofsuch liquids as hydraulic fluids, cooling media and lubricants in theselow temperature ranges. These compounds are also relatively nonvolatileat elevated temperatures due to the high boiling point of thesematerials. Also, certain of the phosphate esters of the invention,particularly the metafluorophenyl phosphate derivatives, have relativelylow pour points, e.g., of the order of F. to F. or lower, which togetherwith the relatively low viscosity of these materials at lowtemperatures, permit the liquid compounds to be pumped without highexpenditure of energy at low temperatures. Moreover, the phosphateesters of the invention have good hydrolytic stability, and do notadversely affect materials, such as metals, e.g., steel, aluminum, andthe like, with which they may be in contact.

The above-noted properties render many of the fluoroaryl phosphateesters hereof, and especially the metafluorophenyl derivatives,particularly useful as hydraulic fluids, lubricants and heat transfermedia, e.g., cooling fluids, in aircraft systems, especially modernhigh-speed aircraft systems.

Those fiuoroaryl phosphate esters of the invention having pour pointsand melting points above 0 F., for example those containing ortho fluoroand/ or para fluoro substituents, can be employed as general industrialhydraulic fluids and lubricants particularly where high fire resistanceand high thermal stability are important characteristics, e.g., in highpressure systems, such as hydro electric turbines, air compressors andhydraulic presses having various sources of ignition which would resultin fire and explosion from leaking hydraulic fluids in the event suchfluids are not adequately fire resistant.

Also, the above-noted relatively higher melting derivatives, andincluding, for example, the o-cresyl substituted phosphate estersaccording to the invention, can

3 be employed as additives in combination with compatible phosphateesters such as the m-fluorophenyl phosphate esters hereof, or otherphosphate esters such as the fluorinated diaryl phosphate esters of thecopending application Ser. No. 364,763 filed May 4, 1964, of Seil et al.now Patent No. 3,308,207, to function as thickeners, lubricity improversor pour point depressants for such esters, e.g., when the latter areemployed as hydraulic fluid base stocks. When so employed as additives,the compounds of the invention are used generally in a proportion ofabout 1 to about 10% by weight of the total composition.

The fluoroaryl phosphate esters of the invention can be produced byreacting a suitable phenol or monofluorophenol compound, or mixturesthereof, with a suitable aryl, e.-g., phenyl or monofluorophenyl,phosphoryl dichloride, or with a suitable diaryl, e.g., diphenyl or bis(fluorophenyl) phosphoryl chloride, preferably in the presence ofpyridine or any other suitable HCl acceptor. The proportion of HClacceptor or pyridine generally employed is usually about equimolar withrespect to the phenol compound employed. Where, for example, a phenyl orfluorophenyl phosphoryl dichloride is used, a proportion of about 2moles of the phenol compound to one mole of the phosphoryl dichloride isemployed. Where, for example, a diphenyl or bis (fluorophenyl)phosphoryl chloride is used, a proportion of about one mole of thephenol compound to one mole of the phosphoryl chloride is utilized.Monofiuorophenyl phosphoryl dichloride and bis(monofiuorophenyl)phosphoryl chloride are the subject of the invention of the copendingapplication Ser. No. 421,641. filed of even date herewith, of Robert H.Boscnan and James P. Holder, and the method of preparation of thesecompounds is described in said application.

The tris(monofiuoroaryl), e.g., tris(monofiuorophenyi), phosphate estersof the invention are prepared by reacting a suitable monofluorophenolcompound with phosphorus oxychloride in a proportion of about 3 moles ofthe fluorophenol to one mole of POCl The reaction is carried outgenerally by heating the reaction mixture, which may also include anorganic solvent, e.g., benzene, for a period of time, e.g., severalhours, removing the organic phase containing the phosphate esterreaction product, preferably washing, and then drying such organicmaterial, and distilling this material, usually at low pressure, toseparate the phosphate ester present from excess phenol compound, and toremove water and any organic solvent present.

Specific examples of fiuoroaryl phosphates of the invention are asfollows:

if l Q I? @WQ) l C C t Q O l (11) F CH3 fil l c z (14) F CH3 l? WG C113(15) F CH3 CH (10) CH3 F Some of the preferred compounds of theinvention are compounds (1) to (5) above. Compound (1) especiallypossesses a combination of viscosity characteristics, pour point, liquidrange, thermal stability, and lubricity, rendering such compoundparticularly valuable as a hydraulic fluid, lubricant and coolingmedium, and as especially suitable for use in hydraulic systems ofaircraft.

The following are examples of preparation and use of the compounds ofthe invention:

Example 1.-Bis(m-fluorophenyl) phenyl phosphate To a mixture of 117.7 g.(1.05 moles) of m-fiuorophenol, 87.0 g. (1.10 moles) of pyridine and 400ml. of benzene was added dropwise with stirring 105.5 g. (0.500 mole) ofre-distilled phenylphosphoryl dichloride. The temperature was maintainedat 15-20 C. during the addition, which was complete in 2 hours. Themixture was heated to reflux temperature and refluxed overnight. Themixture was then cooled and poured into 700 ml. of

water. The bottom aqueous layer was withdrawn from the upper organiclayer and was extracted with three 125 ml. portions of ether. The etherextracts were added to the organic layer, which was then washed withsuccessive 100 ml. portions of 5% hydrochloric acid and 5% sodiumbicarbonate, then washed with three 60 ml. portions 'of water. Afterdrying over anhydrous magnesium sulfate, the solvents were removed byevaporation on a steam bath.

The residue was distilled at reduced pressure; the main phosphate estherfraction, 147.1 g. (81.2% yield) distilled at 159-160 C. (0.12 mm.mercury).

Analysis-Calculated for C H F O P: C, 59.68; H, 3.62; F, 10.49; P, 8.55.Found: C, 59.85; H, 3.64; F, 9.90; P, 8.49.

The resulting phosphate ester product, compound (1) above, has a densityof 1.325 g./ml. at 77 F., a kinematic viscosity at F. of 416centistokes, and a pour point of -60 F. The compound remains liquid overa broad temperature range. In addition, such phosphate has a thermalstability up to 753 F., high autoignition temperature, good hydrolyticstability, and high fire resistance.

A Shell 4-ball wear test on the phosphate ester of this example, carriedout at 1,200 r.p.m. for 1 hour at 400 F. using a 40 kgm. load for steelon steel, gave a scar diameter of 0.70 mm., indicating that suchphosphate ester has excellent wear properties and excellent lubricity.

An oxidation corrosion test of the phosphate ester of this example onvarious metals was carried out by contacting such ester with therespective metals at 550 F. for 24 hours. The results are noted below inTable I.

TABLE 1 Metal: Corrosion mg./cm. Aluminum +0.02 Steel --0.01 Silver+0.06 Titanium +0.08

Example 2.Tris (m-fluorophenyl) phosphate To a mixture of 24.7 g. (0.221mole) of m-fluorophenol, 18.3 g. (0.231 mole) of pyridine and 35 ml. ofbenzene was added dropwise with stirring 10.7 g. (0.070 mols) ofredistilled phosphorus oxychloride. The temperature was maintained at 15-25 C. during the addition, which was complete in 45 minutes. Themixture was heated to reflux temperature and refluxed for 22 hours.

The mixture was then cooled and poured into 250 ml. of water. The lowerorganic layer was withdrawn and the aqueous layer was extracted withthree 50 ml. portions of ether. The ether extracts were added to theorganic layer, which was then washed with successive 25 ml. portions of5% hydrochloric acid, 5% sodium bicarbonate, and water. After dryingover anhydrous magnesium sulfate, the solvents were removed by heatingon a steam bath. The residue Was the distilled at reduced pressure, andthe main product fraction, 20.3 g. (76.2% yield) distilled at 176-179 C.(1 mm. mercury).

AnaIysis.Calculated: C, 58.86; H, 3.18; P, 8.15. Found: C, 57.90; H,3.33; P, 7.90.

The resulting product, consisting essentially of tris(mfluorophenyl)phosphate, compound (2) above, has a pour point below about 60 F., hasgood thermal stability between about 600 and about 800 F., highautoignition temperature in the range of about 900 to about 1,000 F.,good hydrolytic stability and high fire resistance. Such phosphate has awide liquid range and is useful as a base stock component for ahydraulic fluid of an aircraft system and as a lubricant.

Example 3.-m-fluorophenyl p-fluorophenyl phenyl phosphate To a mixtureof 35.3 g. (0.315 mole) of m-fluorophenol, 35.3 g. (0.315 mole) ofp-fluorophenol, 52.2 g. (0.660 mole) of pyridine and 250 ml. of benzenewas added dropwise with stirring 63.3 g. (0.300 mole) of phenylphosphoryl dichloride. The temperature was maintained at 1015 C. duringthe addition, which was complete in one hour and 15 minutes. The mixturewas heated slowly to reflux temperature and refluxed for 18 hours.

The mixture was then cooled and poured into 400 ml. of water. The loweraqueous layer was withdrawn and extracted with two ml. portions and one50 ml. portion of ether. The ether extracts were added to the organiclayer which was then washed with 100 ml. of 5% hydrochloric acid, 100ml. 5% sodium bicarbonate and one 100 ml. portion and two 50 ml.portions of water. After drying over anhydrous magnesium sulfate, thesolvents were removed by heating on a steam bath. The residue was thendistilled at reduced pressure. The main product fraction, 95.4 g. (87.7%yield) distilled at l68169 C. (0.25 mm. mercury).

The product consisting essentially of compound (3) above, m-fluorophenylp-fluoro'phenyl phenyl phosphate, has a pour point of 50 F., a kinematicviscosity at 0 F. of 744 centistokes, good thermal stability, highautoignition temperature, good hydrolytic stability, and high fireresistance. Such phosphate, having a wide liquid range, is useful as abase stock for a hydraulic fluid of an aircraft system.

Example 4.m-fluorophenyl diphenyl phosphate To a mixture of 62.1 g.(0.660 mole) of phenol, 52.2 g. (0.660 mole) of pyridine and 250 ml. ofbenzene was added dropwise with stirring 68.7 g. (0.300 mole) ofm-fluorophenyl phosphoryl dichloride. The temperature was maintained at10-17 C. during the addition, which was complete in one hour and 45minutes. The mixture was heated slowly to reflux temperature andrefluxed for 35 hours.

The mixture was then cooled and poured into 500 ml. of water. The upperorganic layer was withdrawn and the aqueous layer was extracted withthree 100 ml. portions of ether. The ether extracts were added to theorganic layer, which was then washed with 100 ml. of 5% hydrochloricacid, 100 ml. of 5% sodium bicarbonate, and three 50 ml. portions ofwater. After drying over anhydrous magnesium sulfate, the solvents wereremoved by heating on a steam bath. The residue was then distilled atreduced pressure. The main product fraction, 92.5 g. (89.3% yield)distilled at 168-170 C. (0.19-0.23 mm. mercury).

Analysis.-Calculated for C H FPO C, 62.80; H, 4.10; F, 5.52; P, 9.00.Found: C, 62.88; H, 4.09; F, 5.29; P, 8.90.

The resulting product consisting essentially of compound (4) above,m-fluorophenyl diphenyl phosphate, has a viscosity at 100 F. of 11.4centistokes, a pour point of about 10 F., a thermal stability up toabout 692 F., high autoignition temperature, good hydrolytic stabilityand high fire resistance. Such phosphate ester is useful as a fireresistant thermally stable hydraulic fluid 0r lubricant for generalindustrial purposes, e.g., in a hydraulic press or as a compressorlubricant.

Example 5.Bis (p-fluorophenyl)'phenyl phosphate To a mixture of 70.6 g.(0.630 mole) of p-fluorophenol plete in one hour. The mixture was heatedslowly to reflux and refluxed for 17 /2 hours.

The mixture was then cooled and poured into 400 ml. of water. The loweraqueous layer was withdrawn and extracted with three 100 ml. portions ofether. The ether extracts were added to the organic layer, which wasthen washed with 100 ml. of 5% hydrochloric acid, 100 ml. of 5% sodiumbicarbonate, and three 50 ml. portions of water. After drying overanhydrous magnesium sulfate, the solvents were removed by heating on asteam bath. The residue was then distilled at reduced pressure. The mainproduct fraction, 95.3 g. (87.7% yield), distilled at 178l80 C.(0.22-0.26 mm. mercury).

AIzaIysis.Calculated for C H F O P: C, 59.68; H, 3.62; P, 8.55. Found:C, 59.56; H, 3.64; P, 8.23.

The product produced, consisting essentially of compound (5) above,bis(p-fluorophenyl) phenyl phosphate, has a melting point of about 40(1., good thermal stability, high autoignition temperature, goodhydrolytic stability, and high fire resistance. Such phosphate is usefulas a base stock for a hydraulic fluid or as a lubricant in systemsoperating at elevated temperatures above about 110 F.

Table 11 below shOWs a comparison of some of the physical properties ofthe phosphate esters of the inven tion, compounds (1) to (5), producedin Examples 1 to 5 above.

containing at least one m-phenyl group in the triaryl phosphate ester,generally have low pour points, noting particularly compounds (1) to (3)of the table, and that such compounds have relatively low viscosity atF. and below, rendering such compounds useful as hydraulic fluids,lubricants and cooling media at temperatures below 0 F., as previouslynoted, as well as at elevated temperatures of the order of about 600 toabout 800 F., due to their high thermal stability. Of particularsignificance, it is noted that compound (3) having one m-fluorophenyland one p-fiuorophenyl group has a low pour point, as compared tocompound wherein the mfluorohenyl group of compound (3) is replaced byan additional p-fluorophenyl group, and which has a high melting point.This clearly indicates the influence of the preferred m-fluoroa-ryle.g., m-fluorophenyl, group in the triaryl phosphate esters of theinvention.

Example 6.Bis(m-fiuorophenyl) p-fluorophenyl phosphate The procedure ofExample 1 is substantially repeated, employing in place of phenylphosphoryl dichloride the same molar proportion of p-fluorophenylphosphoryl dichloride, to thereby obtain compound ('6) above as product,bis (m-fluorophenyl) p-fluorophenyl phosphate.

Example 7.Bis(m-fluorophenyl) m-cresyl phosphate The procedure ofExample 1 is substantially repeated, except employing in place of thephenyl phosphoryl dichloride the same molar proportion of meta cresylphosphoryl dichloride. The product obtained is compound (11) above,bis(m-fluoropheny-l) m-cresyl phosphate.

Example 8 A mixture is prepared consisting of 90% by weight of compound(4), m-fluorophenyl diphenyl phosphate,

and 10% by weight of compound (5), bis(p-flourophenyl) phenyl phosphate.

The resulting mixture has improved liquid range as compared to eithercomponent of such mixture.

Such mixture is effective as a hydraulic fluid and lubricant in aircraftsystems.

Example 9 A mixture is prepared consisting of by weight of1,1,5-trihy'droperfluoropentyl diphenyl phosphate and 5% by weight ofbis(p-fluorophenyl) phenyl phosphate. The diphenyl phosphate ester aboveis described in the above copending application. The resulting mixturehas improved lubricity and lower pour point as compared to the abovediphenyl phosphate ester alone, and is useful as a hydraulic fluid of anaircraft system.

From the foregoing, it is seen that the invention provides a novel classof fluoroaryl, e.g., fluorophenyl, phosphates which are designedparticularly for use as base stocks or base stock components oradditives of hydraulic fluids, lubricants and heat transfer or coolingmedia, for aircraft systems and for industrial use.

While we have described particular embodiment of our invention for thepurpose of illustration, it should e understood that variousmodifications and adaptations thereof may be made within the spirit ofthe invention, as set forth in the appended claims.

We claim: 1. A phosphate ester having the formula ll/ ROP where R is amember selected from the group consisting of monofluorophenyl,monofluorocresyl and monofluoroxylyl, and R and R are each a memberselected from the group consisting of phenyl, cresyl, xylyl,monofluorophenyl, monofluorocresyl and monofluoroxylyl.

2. A phosphate ester as defined in claim 1, wherein at least one of saidgroups R and R" is monofluorophenyl.

3. A phosphate ester as defined in claim 1, wherein at least one of saidgroups R and R" is phenyl.

4. A phosphate ester as defined in claim 1, wherein at least one of saidgroups R and R is cresyl.

5. A phosphate ester as defined in claim 1, wherein R ismonofluorophenyl and R and R are each phenyl.

6. A phosphate ester as defined in claim 1, wherein R ismonofluorophenyl, R is monofluorophenyl and R is phenyl.

7. A phosphate ester as defined in claim 6, wherein at least one of saidgroups R and R is m-fluorophenyl.

8. A phosphate ester as defined in claim 1, wherein R, R and R are eachmonofluorophenyl.

9. A phosphate ester as defined in claim 8, wherein at least one of saidgroups R, R and R" is m-fluorophenyl.

10. A phosphate ester as defined in claim 8, wherein at least two ofsaid groups R, R and R are each mfluorophenyl.

11. Bis(mfluorophenyl)phenyl phosphate.

12. Tris(m-fluorophenyl) phosphate.

13. m-Fluorophenyl p-fiuorophenyl phenyl phosphate.

14. m-Fluorophenyl diphenyl phosphate.

15. Bis(p-fluorophenyl)phenyl phosphate.

References Cited UNITED STATES PATENTS 2,033,916 3/1936 Bass 260-9662,727,058 1 2/1955 Conly 260950 2,754,316 7/1956 Conly 260955 CHARLES E.PARKER, Primary Examiner.

B. BILLIAN, A. H. SUTTO, Assistant Examiners.

